Modeling the chemical origin of CO2

There are two major issues the migration of carbon dioxide into a reservoir rock. It can replace valuable hydrocarbons. Also, reservoirs need high-cost equipment if they have high contamination of CO₂. The generation of CO₂ within the source rock environment can happen through two kinetics: the thermal generation from organic matter kerogen, and the dissolution of carbonates.

There is a third source of carbon dioxide, but exterior to a basin. The CO₂ migrated from the mantle. This kind of modeling can be biased to the positioning of carrier faults – not even certain – at the base of the basin.

Considering just the elements internal to the model, we work in an area offshore of the Campos Basin. The main source rock is a thinly laminated lacustrine calcareous black shale. Well samplings suggest the source rock is 19% composed of carbonate. For the sake of accuracy, it is important to understand the share of each kinetics when modeling the contamination of CO₂.

A model employing two kinetics can return the CO₂ saturation with labels of the origin of each species. Comparison of both fractions at all cells of the working model show a higher overall saturation at the Aptian-Barremian layers (blue dots of the plot). Surprisingly, the contribution originated from the dissolution of carbonates is higher than the contribution from the thermal transformation of kerogen.